docs: def getPhysicalMinimum(self,chn=None):
          """
          Returns the minimum physical value of signal edfsignal.
  
          Parameters
          ----------
          chn : int
              channel number
  
          Examples
          --------
          >>> import pyedflib
          >>> f = pyedflib.data.test_generator()
          >>> f.getPhysicalMinimum(0)==-1000.0
          True
          >>> f._close()
          >>> del f
  
          """
          if chn is not None:
              if 0 <= chn < self.signals_in_file:
                  return self.physical_min(chn)
              else:
                  return 0
          else:
              physMin = np.zeros(self.signals_in_file)
              for i in np.arange(self.signals_in_file):
                  physMin[i] = self.physical_min(i)
              return physMin